Cerebral palsy develops when a young brain is damaged or doesn’t form properly, either during pregnancy, during birth, or in the first years of life. It is not a single event but rather the result of one or more disruptions to brain development. About 85 to 90 percent of cases are congenital, meaning the cause occurred before or during delivery. The remaining 10 to 15 percent are acquired after birth, typically from infection or injury in early childhood.
Roughly 1 in 345 children in the United States has cerebral palsy, making it the most common motor disability in childhood. Despite decades of research, pinpointing the exact cause in any individual child remains difficult because multiple risk factors often overlap.
What Happens Inside the Brain
Cerebral palsy is the outcome of brain damage, not a disease that progresses over time. The damage is permanent, but it doesn’t get worse as a child grows. Four main types of brain disruption can lead to it:
- White matter damage. The most common cause. White matter carries signals between different brain regions, and when cells in this tissue die, especially near the fluid-filled spaces deep in the brain, movement and coordination suffer. Premature infants are particularly vulnerable because their white matter is still fragile and developing.
- Oxygen deprivation. When a baby’s brain is starved of oxygen, whether from placental problems, a complicated delivery, or other events, the resulting injury can affect the areas that control movement.
- Bleeding in the brain. Hemorrhages in or around the brain can destroy tissue and disrupt normal development. Premature and low-birth-weight babies face the highest risk.
- Abnormal brain formation. Gene changes can interrupt how the brain grows and organizes itself during pregnancy, leading to structural differences that cause cerebral palsy symptoms.
Causes Before and During Birth
Most cerebral palsy traces back to something that went wrong while the baby was still developing in the womb. Maternal infections during pregnancy are a well-established risk. When a pregnant person contracts certain infections, the resulting inflammation or direct infection of the fetus can damage developing brain tissue. Rubella, cytomegalovirus, and toxoplasmosis are among the infections most closely linked to fetal brain injury.
Problems with the placenta can also reduce the baby’s oxygen and nutrient supply over time. Blood clotting disorders in the mother, placental abruption, and other complications that compromise blood flow all raise the likelihood of brain damage before delivery even begins.
Birth complications get a lot of attention, and oxygen deprivation during labor is a real cause. However, researchers now understand that pure birth asphyxia accounts for a smaller share of cases than previously believed. In many births that appear traumatic, the brain may have already been vulnerable due to prenatal factors, and the stress of delivery becomes the final insult rather than the sole cause.
Prematurity and Low Birth Weight
Being born too early or too small is one of the strongest risk factors. Babies born before 32 weeks of gestation have significantly higher rates of cerebral palsy because their brains are at a critical stage of development and are highly susceptible to bleeding and white matter injury.
Birth weight tells a similar story. A large population-based study in Taiwan found that infants born weighing less than 1,000 grams (about 2.2 pounds) were nearly 12 times more likely to develop cerebral palsy compared to those born at a normal weight. Babies between 1,000 and 1,499 grams had about 5.5 times the risk, and those between 1,500 and 1,999 grams had roughly 3.4 times the risk. The relationship is a clear gradient: the smaller the baby, the greater the vulnerability.
Multiple Births Raise the Risk
Twins, triplets, and higher-order multiples face elevated risk largely because multiple pregnancies are more likely to result in premature delivery and low birth weight. The numbers are striking. In one study, the prevalence of cerebral palsy was 0.9 percent among twins, 3.1 percent among triplets, and 11.1 percent among quadruplets. When researchers looked at the chance that at least one child in the pregnancy would have cerebral palsy, the figures rose to 1.5 percent for twins, 8 percent for triplets, and nearly 43 percent for quadruplets.
Genetics Play a Larger Role Than Expected
For years, cerebral palsy was thought to be almost entirely caused by environmental events like oxygen loss or infection. That view is shifting. A landmark study from Harvard Medical School found that up to 1 in 4 patients with cerebral palsy had an underlying genetic condition. Among children with CP who had no other known risk factors, 29 percent carried a causative genetic variant. Even among children who did have established risk factors like prematurity, 15 percent still had a genetic cause identified through sequencing.
This doesn’t mean cerebral palsy is inherited in the traditional sense. Many of these mutations are “de novo,” meaning they arise spontaneously rather than being passed down from parents. But the finding suggests that some children’s brains may be genetically predisposed to injury, which helps explain why two babies can experience similar birth complications yet only one develops cerebral palsy.
Acquired Cerebral Palsy After Birth
A smaller but important group of children develop cerebral palsy from damage that occurs after birth, typically within the first two years. The most common causes are infections that inflame the brain, such as meningitis and encephalitis, and physical injury to the head. Severe, untreated jaundice in newborns can also cause a specific type of brain damage that leads to cerebral palsy affecting movement control.
Some cases of acquired cerebral palsy are preventable. Vaccinating children against bacterial infections that cause meningitis, including Haemophilus influenzae type B and Streptococcus pneumoniae, reduces one important risk. Treating newborn jaundice promptly with light therapy prevents the buildup of bilirubin that can damage the brain. Using proper car seats and preventing falls reduces the risk of traumatic brain injury in infants and toddlers.
Early Signs to Watch For
Signs of cerebral palsy typically appear in the first few months of life, though many children aren’t formally diagnosed until age 2 or later. The earliest clues involve developmental delays: being slow to roll over, sit up, crawl, or walk. Unusual muscle tone is another hallmark. A baby may feel unusually stiff or unusually floppy, or alternate between the two.
Before 6 months of age, specific signs include an inability to hold up the head when lifted from lying down, legs that stiffen or scissor when the baby is held upright, and a tendency to constantly arch the back and neck as if pushing away. Some infants use one side of the body noticeably more than the other when reaching or moving, which can signal that one side of the brain has been affected.
No single test confirms cerebral palsy. Diagnosis relies on observing a child’s movement patterns over time and, in many cases, brain imaging to look for the type of damage described above. The earlier it’s identified, the sooner therapies can begin to help a child build strength, coordination, and independence.